RESUMO
The formation of a thin layer, the so-called Joint Oxyde-Gaine (JOG), between the (U,Pu)O2 fuel pellets and the cladding has been observed in fast neutron reactors, due to the accumulation of volatile fission products. Cs2MoO4 is known to be one of the major components of the JOG, but other elements are also present, in particular tellurium and palladium. In this work, an investigation of the structural and thermodynamic properties of Cs2TeO4 and Cs2Mo1-xTexO4 solid solution is reported. The existence of a complete solubility between Cs2MoO4 and Cs2TeO4 is demonstrated, combining X-ray diffraction (XRD), neutron diffraction (ND), and X-ray absorption spectroscopy (XAS) results. High-temperature XRD measurements were moreover performed on Cs2TeO4, which revealed the existence of a α-ß phase transition around 712 K. Thermal expansion coefficients were also obtained from these data. Finally, phase equilibra points in the Cs2MoO4-Cs2TeO4 pseudobinary phase diagram were collected using differential scanning calorimetry and used to develop a thermodynamic model for this system using a regular solution formalism.
RESUMO
Sss1p, an essential component of the heterotrimeric Sec61 complex in the ER (endoplasmic reticulum), is a tail-anchored protein whose precise mechanism of action is largely unknown. Tail-anchored proteins are involved in many cellular processes and are characterized by a single transmembrane sequence at or near the C-terminus. The Sec61 complex is the molecular machine through which secretory and membrane proteins translocate into and across the ER membrane. To understand the function of the tail anchor of Sss1p, we introduced mutations into the tail-anchor sequence and analysed the resulting yeast phenotypes. Point mutations in the C-terminal hydrophobic core of the tail anchor of Sss1p were identified that allowed Sss1p assembly into Sec61 complexes, but resulted in diminished growth, defects in co- and post-translational translocation, inefficient ribosome binding to Sec61 complexes, reduction in the stability of both heterotrimeric Sec61 and heptameric Sec complexes and a complete breakdown of ER structure. The underlying defect caused by the mutations involves loss of a stabilizing function of the Sss1p tail-anchor sequence for both the heterotrimeric Sec61 and the heptameric Sec complexes. These results indicate that by stabilizing multiprotein membrane complexes, the hydrophobic core of a tail-anchor sequence can be more than a simple membrane anchor.
